Z28ELECTRICIAN

I installed the new opti and checked all the vent hoses. The vehicle runs alot better and no more DTCs being set. The car still won't idle. It has always had a rough idle(cam) but now it stalls when it tries to idle.
Is there any sort of idle learn procedure Im missing.
The desired idle set to 850rpm, and the learned idle says 32.
BTW I replaced the idle air motor today just to rule out.

GaryDoug

I have never discovered what exactly the "learned" or "min" idle value represents, but I doubt it is very important to your issue. The IAC position is the meaningful one that indicates the current position/performance. The range is 0-160. If you see either of those numbers in the scan data, it means the IAC valve is at its lower (0) or upper limit (160). If zero, the pcm is trying to drop the rpm and couldn't get to the target, 160 means it was trying to raise the idle and it hit the max before it got to the target rpm. Ideally the target idle speed value in the scan data should be very close to the actual rpm.

4th Gen LT1 F-body Tech Articles

Z28ELECTRICIAN

It's at 160. Other than its trying to raise the rpm what else does that tell you. Like I said earlier it has a new IAC motor. Could there be an open if it's at 160 and still won't idle.
Again, Thanks for the help and advise, getting really stressed right now.
Also, just took the car for a test hit and it ran awesome as it always did on or off boost.

Injuneer

What is the idle speed?

The scanner can only show you the position the PCM is trying to set the valve at. There is no feedback as to the actual valve position. If you have a new valve and it's the correct one, could be a problem with the wiring. Also, did you extend the pintle to the correct length before installing? There is an IAC learn procedure. Have you tried that? Go to shbox.com , tech page, how to section for the procedure.

Something may be blocking air flow through the idle air passages. Does the throttle body have an aftermarket "airfoil"? Some of those block the idle air opening. Or, do you have an aftermarket throttle body? Some of those don't have a supplementary idle air passage directly to the intake manifold.

What happens if you extend the throttle blade stop screw to let more air in? As you advance the screw, IAC counts should start to drop. What is your closed throttle position sensor (TPS) voltage? When you start opening the blades, the voltage will start to increase. You don't want it to exceed 0.90 volts. But, some aftermarket TB's require the TPS to be rotated to set it within the correct range. Since the TPS is not adjustable in stock form, it may be necessary to slot the screw holes in the TPS.

Z28ELECTRICIAN

The idle speed is set at 850 RPM.
The vehicle idled fine before engine removal.
It has an Arizona speed and marine TB with adj TPS.
I looked at the idle air passages earlier because I sent the intake to jet hot for coating and I wanted to make sure nothing was obstructed.
As far as setting the pintle length and a Idle learn I didn't do that, I was under the impression that there was no idle learn procedure. I will look up and try tonight.
I can run the screw out and force the car to idle but I don't want to leave it like that for obvious reasons. I will run the screw out and look at the counts as you said and report back to you if the idle learn does not cure this.
As far as TPS voltage at closed throttle I haven't looked but the scan tool show 0 degrees when closed and when I graph the TPS from closed to WOT(KOEO) it is a clean graph with no glitches.
Again thanks for all your support in all this. What angers me is the car ran fine before a routine engine removal with no major mods and now I'm fighting it. I could understand if upon assembly I made major changes but I did this just to dress up the engine bay with things like new paint, braided hoses, canton valve covers,chrome alt, JET hotted a bunch of stuff, simple things like that. I just wanted it to look as good as it runs, or ran for local rod runs, lol.

Z28ELECTRICIAN

Depress accelerator slightly
Start engine, then release accelerator pedal, run engine for 5 seconds
Turn ignition "OFF" for ten seconds
Restart engine and check for proper idle operation
It is NOT recommended to to push or pull on the pintle of an IAC that has been in service. The force required can damage the threads on the worm drive. Also, do not soak the IAC in any liquid cleaner or solvent, as damage may result. When installing a new IAC, you may move the pintle to match the measurement of the old one. The force required to move a NEW valve will not cause damage to it. Use engine oil to lubricate the o-ring. Tighten attaching screws to 27 lb. in.

Note that the 1993 IAC has a square electrical connector and the valve screws into the throttle body, instead of being held on by screws like those of later years.




On second thought this will be tricky since the car wont idle for 5 seconds

Z28ELECTRICIAN

Hey Injuneer just a follow up. First off thanks for all the help. I ended up just going out and putting a 100miles on the car and now it idles and runs great.

Injuneer

Glad it worked out for you.